The 83rd issue of "FRA NEWS," a public relations magazine published by the Fisheries Research and Education Agency, comprehensively explains the reality of "predation" that causes serious damage to the fishing industry and the latest prevention technologies and research results addressing it.
Key Points
Current State of Predation Damage in the Fishing Industry
- Fishing damage to golden-eye snapper and other species in the Izu Islands waters of Tokyo amounts to 100 million to 60 million yen annually
- Predation by sharks and killer whales on tuna longline fishing has become a serious problem worldwide, with total damage reaching 10 billion yen annually based on 2004 data
- Inland water fishery damage by cormorants is estimated at 8.5 billion yen as of 2023
- Clam catches in the Seto Inland Sea have drastically decreased from a peak of 14,424 tons in 1983 to a record low of 514 tons in 2023
Demonstration Research on Clam Predation Countermeasures
- Black sea bream has the most impact on predatory fish in the Seto Inland Sea, with 2023 catches totaling 5,106 tons nationwide, of which the Seto Inland Sea accounts for 4,215 tons
- Experiments with protective nets in Yamaguchi Bay confirmed that clam habitat density inside nets was significantly higher compared to outside
- Installation of protective nets was demonstrated to be effective in preventing the disappearance of clams in tidal flats and continuing fishing production
- In Hatsukaichi City, Hiroshima Prefecture, compartment fishing and protective nets are successfully protecting clam resources through fishery management
Fishing Damage by Sharks and Countermeasure Technologies
- Sharks possess organs called ampullae of Lorenzini that can sense weak electrical fields to locate prey
- Technologies have been developed to repel sharks by attaching metals, electronic circuits, or magnets that generate electric fields near fishing hooks
- Shark deterrent devices have been commercialized for divers and surfers, but challenges remain as responses vary by shark species
- Attempts are being made to use chemicals produced when sharks decay as repellents, utilizing sharks' keen sense of smell
Prevention Measures for Stream Fish Predation
- Infrared cameras confirmed that grey herons gather and prey on stream fish from just one day after release
- Experiments using ponds revealed that approximately 82% of released fish were eaten by large fish, revealing serious damage
- Installation of simple shelters made from bundled tree branches successfully reduced predation to approximately 20%
- In Nikko City, Tochigi Prefecture, initiatives combining disaster prevention education are being conducted through school lessons on creating shelters for char
New Technologies for Cormorant Countermeasures
- Developed "capture by fishing hook" technology that can be safely implemented even in areas where firearms cannot be used
- Constructed a "flight recorder" system that attaches GPS loggers to captured cormorants to track behavior in real time
- Cormorants have a habit of regular sun-drying, during which GPS loggers are also charged
- Obtained behavioral records are shared at regional councils and utilized for planning efficient deterrence measures
The article demonstrates the severity of predation problems facing the fishing industry with specific damage amounts, and emphasizes the importance of efforts to realize sustainable fisheries while coexisting with wildlife by introducing practical countermeasure technologies developed by various research institutions.